I have upper and sometimes lower abdominal pain when i'm running or doing any high intensity sport. what could this be? i also feel like its harder to take a fully deep breath altough i don't have breathing problems and i'm also perfectly healthy?

Without more history, it is hard to be able to know for sure what is causing your abdominal pain. As it happens with vigorous exercise, it would seem likely to be muscular. Even difficulty with deep breathing can relate to a muscle issue. However, some breathing problems like exercise induced asthma can present in subtle ways. For such concerns, best to get a good history and examination.